The Colorado Potato Beetle (Leptinotarsa decemlineata), often called the CPB, is a common insect known for being a significant agricultural pest. This beetle feeds heavily on plants in the nightshade family, particularly potatoes, making quick and accurate identification important for gardeners and farmers. Recognizing this insect involves examining the distinct patterns and body shapes of its adult form and its immature stages.
Defining Features of the Adult Beetle
The adult Colorado Potato Beetle is immediately recognizable by its striking shell pattern. The body is broadly oval, highly convex, and notably hard-shelled, giving it a stout, humpbacked appearance. These beetles typically measure between 6 and 11 millimeters in length, which is roughly the size of a thumbnail.
The coloration consists of a yellowish-white to orange-yellow base, with a pattern of black stripes running lengthwise down the wing covers (elytra). The species name decemlineata refers to the ten bold, black stripes—five on each elytron—which are the most distinct feature. The area behind the head, known as the prothorax, is also marked with irregularly shaped black spots and two short lines near the center.
Identifying the Immature Stages
The immature life stages are often the most destructive forms of the beetle. The cycle begins with the eggs, which are small, oval, and bright yellow to orange, measuring about 1 millimeter long. Females lay these eggs in clusters of 10 to 60, almost exclusively on the underside of host plant leaves.
Once hatched, the larvae are soft-bodied, plump, and noticeably humpbacked. The newly emerged larvae are dark red, but they quickly transition to a pinkish-orange or salmon color as they grow through their four development stages. A defining characteristic is the presence of two rows of prominent black spots along each side of the body. In the final larval stage, they can reach up to 15 millimeters in length before dropping to the soil to pupate.
Common Insects Mistaken for Potato Beetles
Several other insects are sometimes confused with the Colorado Potato Beetle, but close visual inspection reveals clear differences. The most common look-alike is the False Potato Beetle, Leptinotarsa juncta, which shares a similar size and striped pattern. A key distinction is that the CPB has ten fully separate black stripes on its wing covers.
The False Potato Beetle, however, often has a reddish-brown stripe replacing one of the light-colored stripes in the center of the elytron, and the black lines may merge near the wing tip. Another similar species is the Three-lined Potato Beetle, which is more slender and has thinner black stripes.
The yellow-orange eggs of the CPB are sometimes confused with those of certain lady beetles. However, CPB eggs are consistently found on potato or other nightshade leaves, whereas lady beetle eggs are typically laid near aphid colonies on various plants.